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diff rtc.h @ 30:435c6330896c

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Set tv_usec in gettimeofday() by using the prescaler counter.
author Daniel O'Connor <darius@dons.net.au>
date Tue, 27 Nov 2012 13:19:11 +1030
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--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rtc.h	Tue Nov 27 13:19:11 2012 +1030
@@ -0,0 +1,11 @@
+/* RTC period = RTCCLK/RTC_PR = (32.768 KHz)/(32767+1) */
+#define RTC_PRESCALE 32768
+
+/* usec = x * 1e6 / 32768
+ * However, 1e6 / 32768 = 30.5 which will result in a large error (max of 15807 usec), so we use
+ * some extra bits to get more precision. We can scale up until 32768 * n is > 2^32.
+ * This results in a maximum error of 1 usec.
+ */
+#define RTC_PS2USEC(x) ( \
+	(uint32_t)( \
+	    (uint32_t)((1 << 9) * (1e6 / RTC_PRESCALE)) * (RTC_PRESCALE - (x))) >> 9)